Polyarylene sulfide (hereinafter abbreviated to PAS) represented by polyphenylene sulfide (hereinafter abbreviated to PPS) has excellent properties as an engineering plastic such as excellent heat resistance, barrier property, chemical resistance, electric insulation properties, and moisture heat resistance, and are used mainly for injection and extrusion molding applications, for example, various electrical and electronic components, mechanical components, automobile components, films, fibers and the like.
Of these, in injection molding applications, a filler is often added to produce various properties such as increase in strength and improvement in electrical properties. Particularly, for the purpose of increasing strength, addition of reactive compounds such as coupling agents together with a filler is widely known to maximize the reinforcement effects. However, in the reaction of dichlorobenzene with a sulfidizing agent, which is a general method of producing PPS, a typical example PAS, the main chain backbone has a benzene ring and sulfur as main components and has no sufficient functional group, and thus there were limitations on improving the reinforcement effects of a filler by adding reactive compounds such as coupling agents. Although PAS itself is a polymer having excellent chemical resistance, its resin composition has a problem that the mechanical properties significantly decrease after a chemical treatment since the filler has low adhesiveness.
Therefore, Japanese Unexamined Patent Publication (Kokai) No. 2001-279097 (Claims) discloses improvement in mechanical properties by selectively using PAS having a specific carboxyl group.
Japanese Unexamined Patent Publication (Kokai) No. 5-170907 (Claims) discloses a producing method in which a denaturating agent selected from compounds having a carboxyl group, a mercapto group, or a disulfide group at the same time in the molecule is reacted during melt kneading to prepare PPS having a carboxyl group, to improve the physical properties by introducing a reactive functional group into PPS.
Japanese Unexamined Patent Publication (Kokai) No. 4-018422 (Claims) and Japanese Unexamined Patent Publication (Kokai) No. 4-372624 (Claims) disclose a method of introducing a carboxyl group by thermally reacting an amino group-containing PAS prepared in advance with phthalic acid chloride or acid anhydride, aiming to improve the adhesiveness to metals and the compatibility with other polymers.
However, in the method according to Japanese Unexamined Patent Publication (Kokai) No. 2001-279097 (Claims), only PAS having poor mechanical properties was obtained because of a small amount of carboxyl groups.
In the method according to Japanese Unexamined Patent Publication (Kokai) No. 5-170907 (Claims), the amount of introduction of carboxyl groups is unknown, and properties such as mechanical properties are not disclosed at all, and thus it is difficult to produce the amount of carboxyl groups necessary for significant improvement in mechanical properties and chemical resistance. Furthermore, the absorption peak derived from carboxyl groups in the FT-IR spectrum disclosed is very small, and it is speculated that almost no carboxyl group is introduced.
However, in the methods according to Japanese Unexamined Patent Publication (Kokai) No. 4-018422 (Claims) and Japanese Unexamined Patent Publication (Kokai) No. 4-372624 (Claims), it is expected that a melting point decreases since the side chain having introduced carboxyl groups is bulky, and it is speculated that a resin composition using the PAS is not suitable for applications requiring heat resistance. A decrease in melting point, namely low crystallinity may lead to deterioration of mechanical properties and chemical resistance.